Bertram C D, Macaskill C, Davis M J, Moore J E
School of Mathematics and Statistics, University of Sydney, NSW, 2006, Australia,
Biomech Model Mechanobiol. 2014 Apr;13(2):401-16. doi: 10.1007/s10237-013-0505-0. Epub 2013 Jun 26.
Our published model of a lymphatic vessel consisting of multiple actively contracting segments between non-return valves has been further developed by the incorporation of properties derived from observations and measurements of rat mesenteric vessels. These included (1) a refractory period between contractions, (2) a highly nonlinear form for the passive part of the pressure-diameter relationship, (3) hysteretic and transmural-pressure-dependent valve opening and closing pressure thresholds and (4) dependence of active tension on muscle length as reflected in local diameter. Experimentally, lymphatic valves are known to be biased to stay open. In consequence, in the improved model, vessel pumping of fluid suffers losses by regurgitation, and valve closure is dependent on backflow first causing an adverse valve pressure drop sufficient to reach the closure threshold. The assumed resistance of an open valve therefore becomes a critical parameter, and experiments to measure this quantity are reported here. However, incorporating this parameter value, along with other parameter values based on existing measurements, led to ineffective pumping. It is argued that the published measurements of valve-closing pressure threshold overestimate this quantity owing to neglect of micro-pipette resistance. An estimate is made of the extent of the possible resulting error. Correcting by this amount, the pumping performance is improved, but still very inefficient unless the open-valve resistance is also increased beyond the measured level. Arguments are given as to why this is justified, and other areas where experimental data are lacking are identified. The model is capable of future adaptation as new experimental data appear.
我们已发表的由多个在止回阀之间主动收缩节段组成的淋巴管模型，通过纳入从大鼠肠系膜血管的观察和测量中得出的特性得到了进一步发展。这些特性包括：（1）收缩之间的不应期；（2）压力-直径关系的被动部分的高度非线性形式；（3）滞后和跨壁压力依赖性的瓣膜开启和关闭压力阈值；（4）如局部直径所反映的主动张力对肌肉长度的依赖性。实验上，已知淋巴瓣膜倾向于保持开放。因此，在改进后的模型中，血管对流体的泵送因反流而遭受损失，并且瓣膜关闭取决于首先导致足以达到关闭阈值的不利瓣膜压力降的回流。因此，开放瓣膜的假定阻力成为一个关键参数，本文报告了测量该量的实验。然而，结合这个参数值以及基于现有测量的其他参数值，导致泵送无效。有人认为，由于忽略了微量移液器阻力，已发表的瓣膜关闭压力阈值测量高估了这个量。对可能产生的误差程度进行了估计。通过这个量进行校正后，泵送性能有所改善，但除非开放瓣膜阻力也增加到超过测量水平，否则仍然效率很低。给出了为什么这样做合理的论据，并确定了其他缺乏实验数据的领域。随着新的实验数据出现，该模型能够在未来进行调整。
